Nearly invisible in the water, marine eels in the larval stage could swim right by you and all you’d notice is the slightest movement. Called ‘leptocephalus‘, which means ‘slim head’, eel larva have flattened bodies that contain jelly-like substances on the inside. Unlike many other species, eels remain in the larval stage for quite a while – three months to more than a year.

Some leptochephalus larva have a more solid-looking head, while others are almost entirely transparent. Lay one out in your hand or on a sheet of white paper, and the most you can pick out is usually a bit of muscle fiber on the outside of the eel’s body, and the digestive tube running through the center.

Leptocephalus can swim both forwards and backwards. They appear to feed on tiny particles that float freely in ocean water, often referred to as ‘marine snow’. The longest-known eel larva reaches nearly a foot in length.

Watch the video above to see how easy it is to miss these interesting, transparent little creatures.